By the time Tony Blair left Downing Street, the marriage between new Labour and the public was heading for the rocks. Passions had cooled; the relationship had gone stale; something was needed to rekindle the love affair.

Gordon Brown's arrival as prime minister was the equivalent of the weekend break suggested by marriage counsellors to couples thinking of splitting up. Get away from it all, they say. Leave the kids at home. Remember what it was that you once liked about each other.

And in July and August that's what happened. Brown and the public walked hand-in-hand along the beach at sunset; they ordered the gourmet meal with the bottle of Puligny Montrachet; for the first time in years they even enjoyed themselves when they turned the dimmer switch down.

While the weekend lasted, there was hope that the marriage could once again prosper. Not, of course, with quite the intensity of spring 1997, when the couple could hardly keep their hands off each other, but with the maturity that age and understanding can bring to a relationship. Sadly, the warmth and tenderness faded once the break was over. Back at home, back to the reality of the working week and trying to make ends meet, the public wondered whether Brown had really meant it when he said lessons had been learned and he would change his ways. The talk of a fresh start had been convincing over the roast turbot and crème brûlée; now it seemed like an empty promise. Brown was still leaving the lid off the toothpaste, still to be found slumped in front of the TV watching Match of the Day, still working late in the office five nights a week. His one concession was to buy a sharp suit identical to the one favoured by the posh young man who had moved in next door. Did she fancy him? The public wasn't quite sure, but at least he was different.

That, then, is how things stand. The relationship is not doomed; inertia, if nothing else, may keep the couple together. But this is a rocky patch, and it will take time, effort and luck to get through it. Once the magic has gone, it's hard to get it back.

Take the case of John Major, who had not one honeymoon but two. Major had one big surge in popularity when he took over from Margaret Thatcher and another in the immediate aftermath of his surprise victory in the 1992 election.

Black Wednesday changed all that. From being the decent bloke next door that you might bump into at Homebase, he became the bumbling, over-promoted incompetent who was not up to the job.

Disasters

He was not helped by the fact that Black Wednesday was followed by a string of other disasters - the Iraq Supergun scandal, the closure of half the country's coalmines, the death of James Bulger and higher taxes - but September 16 1992 was the pivotal moment. Up to that point, the country had been willing to live with Major's little foibles; afterwards it was not.

Clearly, the events of the past 10 days are not Labour's Black Wednesday or anything like it, but it may mark the moment when Brown ceases to get the benefit of the doubt. Much will depend on what happens next, with the future - in the words of Donald Rumsfeld - divisible into known unknowns and unknown unknowns. The unknown unknowns could be anything: a military disaster, a terrorist outrage caused by a failure in security, a sleaze scandal, lack of vaccines to deal with a winter flu epidemic. Stuff happens.

Brown needs the unknown unknowns to be kept to a minimum, because he is going to have enough on his plate with the known unknowns. Foremost among these are the state of the economy and the public finances. Like a couple living beyond its means, Britain faces a period of belt-tightening. Real incomes are growing slowly, food and petrol prices are rising, taxes have gone up.

What's more, interest rates have been rising and over the next year an average of 110,000 households each month will come to the end of their fixed-rate mortgage deals taken out before August 2006. Servicing those loans is going to be a lot more expensive unless the Bank of England starts cutting interest rates. There is no indication that Threadneedle Street is in any hurry to do so.

The talk of neighbourhood dinner parties is that house prices have started to fall. Last month's drop in prices reported by the Halifax could be dismissed as a rogue number, but the trend picked up by the Royal Institution of Chartered Surveyors is harder to ignore. Estate agents are the first to know what is happening to bricks and mortar, and the message from the RICS is that the market is weak. Capital Economics believes house prices will fall by 3% next year and by a further 3% in 2009. To be fair, Capital has cried wolf on house prices before, back in 2004-05, but this time it believes there is a far greater chance of a weaker market turning into an outright fall in property inflation.

"Poorer affordability, tighter lending criteria and the outlook for mortgage repossessions all suggest that house prices will be less resilient to a growth slowdown this time around," says Ed Stansfield, Capital's property analyst.

"Mortgage affordability is now 34% worse than its long-term average and 16% worse than in mid-2005. Over the past two years, 25% of borrowers have either put down no deposit or taken a loan of at least 4.5 times their income. Even a modest tightening in lending standards could thus affect a significant share of the property market."

Reluctant

Brown likes to be seen as the nation's breadwinner, putting food on the table for the past decade. Yet the government's own forecasts suggest that the winter will see growth slacken, adding to the pressure on the public finances. The increases in spending for the government's priority areas announced last week were only possible because Labour has imposed pay cuts on public sector workers, announced tight settlements for local government and still allowed borrowing to rise. All three may come back to haunt it over the coming months.

Indeed, it is quite easy to envisage the first real test of Brown's popularity - next May's local elections - coming at the end of a winter pock-marked by disputes with public sector workers and in which a depressed property market has made consumers reluctant to part with their money.

At that point, in spring next year, council tax bills will come plopping through the letter box and they are unlikely to do much for the government's popularity. Indeed, should Boris Johnson somehow manage to beat Ken Livingstone in the London mayoral race, Brown's relationship with the voters may end in an acrimonious divorce.

Brown and Livingstone are the neighbours who have never got on. They have been separated by the political equivalent of a giant Leylandii hedge. It would be paradoxical if it was up to Ken to save New Labour's marriage.